PROJECT SUMMARY Anaphylaxis is a severe allergic reaction that can be rapidly progressing and fatal. In instances where the triggering allergen is not known, establishing the etiology of anaphylaxis is pivotal to long-term risk management. Our recent work has identified a novel IgE antibody response to a mammalian oligosaccharide epitope, galactose-alpha-1,3-galactose (?-gal), that has been associated with two distinct forms of anaphylaxis: i) immediate onset anaphylaxis during first exposure to intravenous cetuximab, and ii) delayed onset anaphylaxis 3-6 hours after ingestion of mammalian food products (e.g., beef and pork). The overarching goal for this proposal is that defining both the cause and the mechanism of ?-gal IgE response, as well as identifying the antigen responsible for the delayed food reactions, will provide insight into the factors that govern allergic responses and control anaphylaxis. Our novel ?-gal-allergic mouse model will allow us to test the central hypothesis that tick bites induce a basophil-dependent, ?-gal specific immune response that, due to unconventional T cell antigen presentation, results in delayed allergic reactions to red meat. The significance of investigating these reactions comes not only from the obvious importance of understanding a novel life-threatening form of food allergy, but also because of the possibility of defining a totally new mechanism for reactions related to an important food substance. Our plan of research focuses on the elucidating the role of immune cells in the murine model, defining the role of tick bites in initiating the IgE and understanding the antigen that appears in the bloodstream 3-6 hours after eating beef, pork or lamb. Our current work has shown that IgE to the carbohydrate alpha-gal is present in a cohort of patients who report delayed anaphylaxis and allergic reactions after eating mammalian meat. We believe that IgE to ?- gal represents a novel cause of food allergy. The specific aims outlined in this proposal are designed to establish the role of tick bites in initiating the ?-gal IgE response (Specific Aim 1), investigate the mechanism for IgE production (Specific Aim 2) and elucidate the mechanism for delayed reactions (Specific Aim 3). Overall, these studies are uniquely positioned to provide insight into a recently recognized allergic response that affects >3,500 patients in the southeastern U.S. as well as identify the molecules present during an allergic reaction and establish a model for ecto-parasitic tick bites initiating an IgE response.